Discharge In Mixture Research Articles

Magnetron discharge in an argon-oxygen mixture for deposition of a titanium oxide film

A discharge in a planar magnetron with a titanium target is studied. It is found that a pressure rise from 2 to 6 mTorr in argon at a constant current increases the intensity of excited argon ion lines by almost 20%. The excitation of neutral titanium atoms is independent of the argon pressure: it depends on only the discharge current. The current-voltage characteristic of the magnetron in an argon-oxygen mixture completely reflects processes proceeding on the target of the magnetron.

Absolute OH density measurements by broadband UV absorption in diffuse atmospheric-pressure He–H2O RF glow discharges

The measurement of radical densities in atmospheric-pressure plasmas has gained increasing importance in recent years in view of their crucial role in many applications. In this paper we present absolute OH density measurements by broadband UV absorption in diffuse atmospheric-pressure RF glow discharges in mixtures of He and H2O. The use of a 310 nm light-emitting diode as a light source and a very high resolution spectrometer (2.6 pm resolution) made the estimation of the total OH density possible by simultaneously measuring the absorption rates of different spectrally resolved rotational lines of the OH(A–X) transition. For different RF powers and water concentrations, OH densities and gas temperatures ranging between 6 × 1019and 4 × 1020 m−3 and 345 and 410 K, respectively, were obtained. The gas temperature Tg was also measured by three different methods. Tg deduced from the rotational temperature of N2(C–B) emission, nitrogen being present as a trace impurity, provided the most reliable value. The rotational temperature Tr of the ground state OH(X) presented values with a maximum deviation of 25 K compared with Tg. To obtain the gas temperature from the emission intensities of OH(A–X) rotational lines, the recorded intensities of different lines must be corrected for the effect of self-absorption inside the plasma.

Comparison of low-pressure DC glow discharge and dielectric barrier discharge in CO2-laser mixture by optical emission spectroscopy

Nowadays the CO2 lasers are used in many technologies, including medicine and material processing industry. Besides original low-pressure low-power lasers pumped by DC glow discharge, the attention is focused on the high power atmospheric pressure lasers. We use optical emission spectroscopy to study both low pressure (from 266 Pa to 1330 Pa) DC glow discharge (DC GD) and the dielectric barrier discharge (DBD) (from 5 kPa to 100 kPa) in mixtures of helium, nitrogen and carbon dioxide used in CO2 lasers.Considering the emission spectrum of the discharges mentioned above, we can find bands of the first and the second positive systems of the nitrogen molecule. From these bands it is possible to deduce energetic balance and the vibrational temperature [1].In our contribution, the vibrational temperature of nitrogen is determined by means of optical emission spectroscopy from the second positive system band of the nitrogen molecule for various discharge currents in DC glow discharge and for various gap widths in DBD. Using these two discharges we covered the whole pressure range from 266 Pa up to atmospheric pressure. The dependence of the vibrational temperature on N2 content in the mixture is also investigated. The vibrational temperature showed a steady decrease with increasing pressure in whole pressure range. It was found, that the vibrational temperature of nitrogen in the DC GD is twice as high as in the DBD, which was attributed to the different nature of discharges.Spectroscopic measurements were complemented with measurements of electric properties of discharges: the longitudinal electric field strength for DC glow discharge and Lissajous' figures for DBD [1,2].

Effect of adding small amount of inductive fields to O2, Ar/O2 capacitively coupled plasmas

Electron energy distribution functions (EEDFs) of low pressure O2 plasma were measured by adding small amount of coil power in a capacitive discharge. When the plasma was generated by bias power only, the measured EEDF showed a bi-Maxwellian distribution. However, when a very small coil power (a few Watts) was added, the EEDF evolved abruptly into a Maxwellian distribution, while the electron density was decreased. In an Ar/O2 mixture discharge, this EEDF evolution to the Maxwellian was also observed at a relatively higher coil power. This abrupt change in EEDFs with a very small coil power appears to be attributed to a combined effect of collisionless heating by capacitive and induced electric fields.

An influence of the electrode emission properties and the gas temperature on the discharge ignition voltage in the mixture of argon with mercury vapor

Kinetics of electrons, ions and metastable excited atoms in the interelectrode gap of a low-current discharge in the argon-mercury mixture is simulated, and the discharge ignition voltage as a function of the temperature and the cathode ion-electron secondary emission rate is calculated. The mixture temperature dependence of the minimum value of the ion-electron secondary emission rate ensuring a given discharge ignition voltage is found.

The microwave and millimeter rotational spectra of the PCN radical (${\rm \tilde X}$X̃3Σ−)

The pure rotational spectrum of the PCN radical (X(3)Σ(-)) has been measured for the first time using a combination of millimeter/submillimeter direct absorption and Fourier transform microwave (FTMW) spectroscopy. In the millimeter instrument, PCN was created by the reaction of phosphorus vapor and cyanogen in the presence of an ac discharge. A pulsed dc discharge of a dilute mixture of PCl(3) vapor and cyanogen in argon was the synthetic method employed in the FTMW machine. Twenty-seven rotational transitions of PCN and six of P(13)CN in the ground vibrational state were recorded from 19 to 415 GHz, all which exhibited fine structure arising from the two unpaired electrons in this radical. Phosphorus and nitrogen hyperfine splittings were also resolved in the FTMW data. Rotational satellite lines from excited vibrational states with v(2) = 1-3 and v(1) = 1 were additionally measured in the submillimeter range. The data were analyzed with a Hund's case (b) effective Hamiltonian and rotational, fine structure, and hyperfine constants were determined. From the rotational parameters of both carbon isotopologues, the geometry of PCN was established to be linear, with a P-C single bond and a C-N triple bond, structurally comparable to other non-metal main group heteroatom cyanides. Analysis of the hyperfine constants suggests that the two unpaired electrons reside almost exclusively on the phosphorus atom in a π(2) configuration, with little interaction with the nitrogen nucleus. The fine structure splittings in the vibrational satellite lines differ significantly from the pattern of the ground state, with the effect most noticeable with increasing v(2) quantum number. These deviations likely result from spin-orbit vibronic perturbations from a nearby (1)Σ(+) state, suggested by the data to lie ~12,000 cm(-1) above the ground state.

Analytical calculation of the gas temperature and time-resolved measurement of the electron temperature of a gas discharge in He and Ne-He mixtures

The gas and electron temperatures were determined in a nanosecond pulsed longitudinal discharge in a new high-temperature discharge tube design developed for a high-power large-volume middle-infrared He-SrBr2 laser. Assuming that the gas temperature varies only in the radial direction, analytical solution of the steady-state heat conduction equation was obtained at uniform power input and, for the first time, for each zone of the discharge tube, namely, discharge zone, ceramic tube, discharge-free zone incompactly filled with zirconia fibers insulation, and quartz tube. The line-ratio optical emission spectroscopy method was used to determine experimentally for the first time the time-resolved electron temperature in the discharge afterglow, namely, measurement of the relative intensities of some He and Ne spectral lines originating from different upper levels. The average values of the electron temperature were also found by averaging the time-resolved electron temperature over the time.

New insights into the structure and chemistry of Titan’s tholins via13C and 15N solid state nuclear magnetic resonance spectroscopy

Tholins are complex C,N-containing organic compounds produced in the laboratory. They are considered to provide materials that are analogous to those responsible for the haze observed in Titan’s atmosphere. These compounds present an astrobiological interest due to their ability to release amino acids upon hydrolysis. Their chemical structure has been investigated using a large number of techniques. However, to date no detailed nuclear magnetic resonance (NMR) study has been performed on these materials despite the high potential of this technique for investigating the environment of given nuclei. Here 13C and 15N solid state NMR spectroscopy was applied to obtain new insights into the chemical structure of tholins produced through plasma discharge in gaseous N2CH4 mixtures designed to simulate the atmosphere of Titan. Due to the low natural abundance of these isotopes, a 13C and 15N-enriched tholin sample was synthesized using isotopically enriched gas precursors. Various pulse sequences including 13C and 15N single pulse, 1H13C and 1H15N cross-polarisation and 1H15N13C double cross-polarisation were used. These techniques allowed complete characterisation of the chemical and structural environments of the carbon and nitrogen atoms. The NMR assignments were supplemented and confirmed by ab initio electronic structure calculations for model structures and molecular fragments.

VUV lamp based on mixtures of inert gases with water molecules pumped by a pulsed-periodic capacitive discharge

The spectral characteristics of the emission in the 140-315 nm range from pulsed-periodic capacitive discharges in mixtures of water vapor and helium and argon are described. In the VUV the most intense bands have maxima at λ = 156.0, 180.3, and 186.0 nm, and in the region of 300–315 nm, at λ = 312.1 and 313.4 nm. The brightness of the emission from the capacitive discharge plasma is optimized with respect to the partial pressures of helium, argon, and water vapor. The electron kinetic coefficients of discharges in argon and water vapor mixtures are calculated for E/N = 1–1000 Td.

Silicon dioxide coating of titanium dioxide nano particles from dielectric barrier discharge in a gaseous mixture of silan and nitrogen

Titanium dioxide nanoparticles are used commonly in various applications due to their high catalytic activity. Many of these applications require subsequent treatments after the deposition of the TiO2 particles. Some of these include thermal processing at high temperatures, e.g. roof tiles. For all of these applications, the crystal structures as well as the microscopic properties are essential. Thus, sintering severely affects the catalytic activity in most of the cases. During thermal processing, the nanoparticles transform from the catalytical highly active anatas structure to the substantially less active rutil structure. This structural change has been found to be significantly retarded when coating the TiO2 nanoparticles with a closed film of SiO2. During the thermal treatment, these films break open, revealing the underlying TiO2 [i]. Thus, the film thickness has to be appropriate for the designated treatment subsequent to the nanoparticle deposition. In this study, we present an approach of SiO2 film deposition making use of silane gas. Pure silane gas is highly demanding on safety standards and technical installations, since it acts self-igniting and highly explosive when getting in contact with air or any oxygen containing gas. Thus, diluted process gases are used for most technical implementations, which contain just about 3% silane in 97% helium, neon, argon, hydrogen or nitrogen. While noble gases and hydrogen are used as dilution for a wide range of applications, the process gas consisting of nitrogen and silane is only implemented for silicon nitride deposition. Nevertheless, this gas should be the most suitable for many applications regarding economics and handling. Closed films produced by dielectric barrier discharges in such mixtures of gases consist of mainly non-stoichiometric silicon nitride, while the other diluted process gases produce metallic silicon films. The deposition of silicon dioxide films is rather complicated, since the silane reacts instantaneously with every oxygen-rich gas. Thus, both gases must not get in contact until they have arrived in front the surface that is to be coated. Most of the existing work found in the literature focuses on the implementation of this condition, to merge the silane and the oxygen right at the surface being coated. Taking a quite different approach, we divided the film deposition into two steps: In the first step, a silicon nitride film was deposited from the process gas with the silane diluted in nitrogen employing a dielectric barrier discharge plasma. As a second step, the silicon nitride film has been tried to convert into silicon dioxide by means of a second plasma discharge using either oxygen for a process gas or even environmental air. All studies have been carried out in an ultra high vacuum apparatus, while the plasma treatments have been carried out up to atmospheric pressure. During the investigations we employed Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS), as well as Atomic Force Microscopy (AFM). The microscopic measurements showed the deposited film to enclose the particles in a Frank van der Merwe – type growth mode. Film thicknesses determined by increased particle diameters in AFM were in good accordance to calculated film thicknesses from XPS peak intensity attenuation. Spectroscopic results show a formation of a silicon nitride film with substoichiometric nitrogen content, though free of oxynitrides. Surface impurities and adsorbates from the ex-situ preparation procedure were strongly removed and seemed to notably increase the growth rate. The second step gained a transformation of the film up to 98% silicon dioxide according to XPS. Remaining carbon impurities from the initially uncleaned surface were removed by both of the oxidizing plasmas. The transformation was found to be even more effective for the air plasma treatment than for the oxygen plasma treatment at a comparable oxygen partial pressure.

Plasma-dust structures in He-Ar DC glow discharge

The gas mixture discharge has a number of features which can appear in experiments with dusty plasma. For example, in the case of a significant difference in atomic masses of ions and atoms, strong anisotropy of the distribution function over ion velocities takes place, which in turn can cause a significant change in properties of dust structures. In this work, experiments on the study of the dust structures in the gas discharge of a mixture of light and heavy gases, i.e., helium and argon, are analyzed. The results of numerical simulation of ion and electron drift in the mixture of these gases and dust particle charging processes are presented.

Optical constants from 370 nm to 900 nm of Titan tholins produced in a low pressure RF plasma discharge

Determining the optical constants of Titan aerosol analogues, or tholins, has been a major concern for the last three decades because they are essential to constrain the numerical models used to analyze Titan’s observational data (albedo, radiative transfer, haze vertical profile, surface contribution, etc.). Here we present the optical constant characterization of tholins produced with an RF plasma discharge in a (95%N2–5%CH4) gas mixture simulating Titan’s main atmospheric composition, and deposited as a thin film on an Al–SiO2 substrate. The real and imaginary parts, n and k, of the tholin complex refractive index have been determined from 370nm to 900nm wavelength using spectroscopic ellipsometry. The values of n decrease from n=1.64 (at 370nm) to n=1.57 (at 900nm) as well as the values of k which feature two behaviors: an exponential decay from 370nm to 500nm, with k=12.4×e−0.018λ (where λ is expressed in nm), followed by a plateau, with k=(1.8±0.2)×10−3. The trends observed for the PAMPRE tholins optical constants are compared to those determined for other Titan tholins, as well as to the optical constants of Titan’s aerosols retrieved from observational data.

Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces, and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β→1; albeit at low βS (< 0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however, some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency-dependent force coefficients. The equivalent damping decreases above and below βS ∼ 0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

On the current density limiting effect in SF6-based mixtures

This paper reports on the investigation of the current density limiting effect in a self-sustained volume discharge in SF6-based mixtures due to a self-action of the discharge current on the media it passes through. The mechanism of this phenomenon in terms of electron-impact dissociation is examined. The argument is advanced that in the planar geometry the limiting effect treated may provoke triggering a spatially uniform volume discharge in the media stated even in the absence of pre-ionization. It is shown that the dissociation mathematics developed by the authors allows the quantitative estimation of the averaged expenditures of energy per formation of a dissociation fragment. Specifically, when applied to pure SF6 this finding enables the assessment of the energy spent for F-atom formation. For the first time the influence of current pulse duration on the discharge voltage has been experimentally revealed. Both thorough qualitative and quantitative considerations including relevant numerical simulation have been performed.

Experimental Investigation on Air-Solid Two-Phase Mixture Discharge under AC Voltage

Multi-phase mixture (MPM) discharge has the common characteristics of randomness with air but more complex. How about the statistical rule of MPM discharge This is not only a fundamental problem for discharge research, but it has its own strong applied and practical characteristics. The air-solid two-phase mixtures(ASTPM) are employed to study and carry out some experiments for investigating the development and breakdown of MPM discharge under AC voltage. The results from experimental data show that the AC breakdown voltage and corona-inception voltage will drop when the solid particles are added to the discharge chamber with different permittivity and volume fraction. And there is no influence in gas flow and the corona current.

Steady-State Partially Constricted Glow Discharge

It is known that, at intermediate gas pressures, the increase in discharge current leads to the constriction of the positive column of the diffuse glow discharge and the formation of the bright filament. Recently, it has been shown that, under certain experimental conditions, constricted and diffuse modes can simultaneously exist in the discharge tube with a constant diameter, i.e., steady-state partially constricted discharge can be realized. Here, we present images and discuss specific features of such kind of discharge in argon-nitrogen mixtures.

Pressure Effects in the Spatial Development of Microcathode Sustained Discharges in Rare-Gas Oxygen Mixtures

It has been recently demonstrated that microcathode sustained discharges (MCSD) are very efficient for the production of large fluxes of singlet delta oxygen (SDO). In this paper, a comparison between MCSD operation in Ar/O2 and in He/O2 mixtures is done. It is shown that, even if SDO production efficiency is theoretically much higher in Ar/O2 mixtures, atmospheric pressure operation is only possible in He-based mixtures.

On stability of self-sustained volume discharge in working mixtures of non-chain electrochemical HF laser

Burning voltage of a self-sustained volume discharge (SSVD) is studied as a function of the specific energy deposition in SF5 with C2—H6 and H2 mixtures, which are working media of a non-chain electrochemical HF laser. It is established that the voltage rises linearly with increasing the specific energy deposition, the relative voltage rise in the SF6—C2H6 mixtures being noticeably higher than in pure SF6 and SF6—H2 mixtures. An assumption is suggested and substantiated on determining the role of molecule dissociation by the electron impact leading to the observed voltage rise. From experimental data we have found approximate energy expenditures of producing dissociation fragments including atomic fluorine in a discharge in pure SF6: Ẽd(F)= 5±1 eV. The values of Ed well agree with literature data obtained by other experimental methods. A conclusion is drawn that the dissociation process is the main mechanism limiting the current density, which implies SSVD realisation without preliminary gas ionisation in working mixtures of a non-chain HF laser and determines a higher stability of the volume discharge in mixtures of SF6 with hydrocarbons (deuterocarbons) as compared to mixtures with hydrogen (deuterium). A method is suggested and substantiated for numerical estimation of the limitation effect of the current density and its influence on the SSVD stability.

Features of the propagation of laminar spherical flames initiated by a spark discharge in mixtures of methane, pentane, and hydrogen with air at atmospheric pressure

Using high-speed digital color cinematography, we studied the propagation of a laminar spherical flame in stoichiometric mixtures of hydrogen, methane, and pentane with air in the presence of additives at atmospheric pressure in constant-volume reactors, and derived quantitative data on the time of formation of a stable flame front. Cellular flames caused by gas-dynamic instability attributable to convective flows arising during the afterburning of gas were observed in hydrocarbon-air stoichiometric mixtures diluted with inert additives. It was found that the effect of additives of carbon dioxide and argon (>10%) and minor additives of CCl4 on the combustion of hydrocarbons, and of propylene on the combustion of hydrogen-rich mixtures, lead to periods of delay in the development of a laminar spherical flame; in addition, additives of propylene promote the combustion of hydrogen poor mixtures.

Electronic spectroscopy of the previously unknown arsenic carbide (AsC) free radical

The previously unknown arsenic carbide (AsC) free radical has been identified in the gas phase through a combination of laser-induced fluorescence (LIF), single vibronic level emission, and stimulated emission pumping (SEP) spectroscopy in a supersonic expansion. The As(12)C and As(13)C isotopologues have been detected as products of an electric discharge in mixtures of arsine (AsH(3)) and carbon dioxide ((12)CO(2) or (13)CO(2)) in high pressure argon. The B (2)Σ(+)-X (2)Σ(+) band system was recorded by LIF spectroscopy and emission transitions from the B state down to the ground state and to the low-lying A (2)Π(i) state were observed. High resolution studies of the B-X 0-0 band by LIF and the B-A 0-0 band by SEP spectroscopy enabled a determination of the molecular structures in the three states. Although CN, CP, and AsC have similar X (2)Σ(+) and A (2)Π(i) states, the B (2)Σ(+) state molecular orbital configuration of CP and AsC differs from that of the CN free radical.